The cell walls of land plants developed under the influence of earth's gravity. Arabinogalactan-proteins (AGPs) are a family of proteoglycans that localize on plasma membranes and in cell walls of higher plants. Recent studies have revealed that the expression levels of genes encoding the core proteins of AGPs are modified by hypergravity, indicating the involvement of AGPs in gravity resistance. A BLAST search in the genome databases of various organisms for genes encoding proteins related to fasciclin-like AGPs (FLAs), found FLAs in land plants including a moss, Physcomitrella patens subsp. patens, but not in the green algae, Chlamydomonas reinhardtii or Volvox carteri. On the other hand, the backbone structure of arabinogalactan moieties of AGPs, β-1,3:1,6-galactan, is widely distributed among organisms and has been confirmed in a species of Chlorellaceae, a snail and a mammal. These facts suggest that acquisition of some AGPs similar to those currently found, and FLAs in particular, was important in the evolution of the resistance of plants to gravitational force. By studying the molecular functions of AGPs under diverse gravitational conditions, we should be able to deepen our understanding of the evolutional process that turned aquatic organisms into terrestrial plants.